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Yard and Garden: Houseplant Pests

AMES, Iowa — Prevention is the first line of defense against houseplant insect problems, according to horticulturists with Iowa State University Extension and Outreach. They share nonchemical methods and appropriate pesticides for controlling houseplant insect problems. To have additional questions answered, contact the ISU Extension and Outreach Hortline at 515-294-3108 or email hortline@iastate.edu. Gardeners also can find answers to common yard and garden questions at the ISU Horticulture Department’s Yard and Garden FAQs website, http://expert.hort.iastate.edu/.

How do I control mealybugs on a houseplant?

Mealybugs on houseplants are difficult to control. Unless the plant is particularly valuable, it’s often best to throw away the infested plant before the insects spread to other houseplants. The standard remedies for houseplant pests can be successful if done with diligence and persistence. On lightly infested plants, pick off individual mealybugs and egg sacs or dab each one with an alcohol-soaked cotton swab. It’s also helpful to syringe plants with a forceful spray of lukewarm water to dislodge the mealybugs from the infested plant.

Mealybugs also can be controlled with insecticide sprays. Use aerosol or hand pump spray products made specifically for houseplants. These may contain any of several different ingredients, including insecticidal soaps, pyrethrin, neem or a synthetic pyrethroid, such as permethrin, bifenthrin or resmethrin. Granular insecticides that you apply to the soil of infested houseplants also may be effective. When using pesticides, carefully read and follow label directions.

How do I control spider mites on houseplants?

Spider mites are a common pest of houseplants. Spider mites use piercing-sucking mouthparts to puncture the plant tissue and feed on the liquid within the cells. In light infestations, the foliage appears to be speckled with very tiny yellowish green spots. The foliage of heavily infested plants often turns greenish yellow and eventually tan or brown. Severely stressed plants often drop some of their leaves. Close examination of infested plants may reveal very fine webbing (produced by the mites) on the leaves and stems.

When mites are present, determine the extent of the infestation and the value of the plant. It’s usually best to discard a plant that is heavily infested with spider mites. Small mite populations can be reduced by washing or syringing infested plant foliage. Move plants outdoors or into the bathtub or shower and then use a forceful spray of water to dislodge the mites from the infested plant.

Several miticides (pesticides that control mites) are available for houseplants. Products can often be purchased at garden centers, greenhouses and other retail businesses. When using pesticides, carefully read and follow label instructions. Keep plants watered and fertilized to promote plant health and to reduce the impact of mite feeding.

How do I control whiteflies on houseplants?

Whiteflies are common insect pests of hibiscus, poinsettia, chrysanthemum and a number of other indoor plants. They are most often noticed when watering or handling a plant. When disturbed, whiteflies flutter about the plant for a short time before returning to the plant.

Whitefly adults are tiny, white, moth-like insects. Female adults lay eggs on the undersides of the plant’s foliage. After five to seven days, the eggs hatch into tiny, pale green, immatures called nymphs. The nymphs crawl a short distance before settling down to feed for two to three weeks. After feeding, the nymphs progress to a non-feeding stage and then finally to the adult stage.

The nymph and adult stages of whiteflies feed by inserting their short, needle-like beaks into foliage and sucking out plant sap. Heavy whitefly infestations often cause stunting or yellowing of leaves, leaf drop and a decline in plant health.

Whiteflies on houseplants are extremely difficult to control. Prevention is the best management strategy. Carefully check newly purchased plants and plants brought indoors from the garden or patio in the fall. Indoors, isolate these plants from other houseplants. Frequently check the new arrivals. Begin control measures at the first sign of a whitefly infestation. One way to reduce the whitefly population on an infested plant is to wash the undersides of the leaves with a moist cloth or sponge. Unfortunately, washing is labor intensive and only practical for small plants.

Insecticides are another control option. Insecticides must be applied uniformly and frequently (at weekly intervals) to the undersides of the plant’s foliage. Apply insecticides specifically labeled for use on houseplants. Carefully read and follow label directions. It’s usually best to discard heavily infested plants to prevent the whiteflies from spreading to other indoor plants.